High strength silicone moldmaking rubber

Transcription

1 Technical Data Sheet High strength silicone moldmaking rubber Features & Benefits Outstanding release properties If required the product cure can be heat accelerated Fast thick section cure at room temperature Medium hardness High inhibition resistance High tear resistance Very high elasticity, for easy removal of complex replica parts Very low shrinkage and good dimensional stability Can be used for high temperature casting applications Can be made thixotropic (non-flowable) for vertical surface replication Fast RTV cure, very fast cure with even, low heat Very low viscosity for easy mixing and de-airing Fast, RTV cure Low durometer hardness Composition Liquid, two-component material consisting of a base and a curing agent, which when mixed, cure at room or elevated temperatures by an additional reaction. Applications is a high strength for detailed reproduction of surfaces and objects for prototype design and production tooling, as well as artistic and renovation applications. Its low durometer also makes it ideal for pad print applications. Typical Properties Specification Writers: These values are not intended for use in preparing specifications. Property Unit Result Base and Curing Agent Applications: Base Viscosity mpa.s 26,000 Color Off white Curing Agent Viscosity mpa.s 140 Page 1 of The Dow Chemical Company. All rights reserved. Form No A

2 Typical Properties (Cont.) Property Unit Result Base and Curing Agent mixture (100:10 by weight) Mixed viscosity mpa.s 13,500 Working time minutes Curing time hours 7 Cured for 24 hours at 23 C (73.4 F) Hardness (Shore A) 25 Tensile strength MPa 7.0 Elongation at break % 850 Tear strength kn/m 23 Relative density at 23 C (73.4 F) 1.12 Linear shrinkage % < 0.1 Moldmaking Rubber Applications: As Supplied Base Color Off-white Viscosity cp 28,000 Curing Agent Color Green Viscosity cp 140 As mixed 100 parts Base to 10 parts Curing Agent by Weight Viscosity 12,800 Specific Gravity 1.12 As Cured 24 hours at 77 F (25 C) Durometer Hardness, Shore A points 26 Tensile Strength psi 1000 Elongation percent 900 Tear Strength, Die B ppi 140 Linear Shrink percent < 0.1 Description How To Use SILASTIC RTV-4250-S Kit Green is a two-component material consisting of SILASTIC RTV-4250-S Base Green and SILASTIC RTV-4250-S Curing Agent Green. A range of materials can be cast into the cured silicone mold: plaster, polyurethane, polyester and other reactive resins are materials typically used. Substrate Preparation The surface of the original should be clean and free of loose material. SILASTIC RTV S Kit Green releases well from most substrates after cure. With porous substrates, a release agent or barrier coat may be needed to seal the surface. Release coatings such as petroleum jelly or others can be used. In all cases, it is advisable to check before casting that no discoloration or adhesion occurs between the product and the original mold or frame. Page 2 of The Dow Chemical Company. All rights reserved. Form No A

3 How To Use (Cont.) Moldmaking Rubber Applications: Application Thoroughly shake/stir the curing agent before use. Weigh out 100 parts of base and 10 parts of curing agent in a clean container. Accurate weighing is essential, as inaccuracies can cause a significant decrease in performance of the cured rubber (the base to curing agent ratio must be between 100:9.5 and 100:10.5). Mix until the curing agent is completely dispersed in the base and a uniform color is obtained. Heat generated by mixing should be minimized. Mix suitably small quantities to ensure adequate working time. (See Table 1.) Entrapped air should be removed in a vacuum chamber, allowing the mixture to completely expand and then collapse. After three additional minutes of vacuum, the mix should be inspected and can be used if free from air bubbles. A volume increase of two to three times will occur on vacuum de-airing of the mixture, so a suitably large container should be chosen. Pour the mixed basic and curing agent onto the master, avoiding air entrapment. The catalyzed mixture will typically cure to a flexible rubber within six to eight hours at room temperature (see Table 1), and the part can be demolded. Heat accelerating the cure is possible, but this will produce some apparent shrinkage of the mold due to differences in the volume contraction on cooling between the silicone rubber and the original. The higher the curing temperature, the greater the likelihood of differences in dimensions. Table 1: Special Use Considerations Regarding Working And Cure Times Temperature F ( C) Typical Working Times, Minutes Typical Time To Demold 50 (10) hours 68 (20) hours 77 (25) 45 7 hours 86 (30) 30 4 hours 104 (40) < minutes 122 (50) < 5 20 minutes Moldmaking Rubber Applications: Inhibition Of Cure All addition-cure silicone elastomers are susceptible to cure inhibition when in contact with certain materials and chemicals. Mixing containers, mold construction materials, masters and release agents should be checked for any inhibition effect before use by properly mixing base and curing agent and applying a small amount against the surfaces. Inhibition has occurred if the elastomer is only partially cured after 16 hours, or has a sticky surface in contact with another material. Amines and sulfur-containing materials are strong inhibitors, as are organotin salts used in condensation-cure silicones. Wet or moist surfaces can cause gas bubbles to form during cure in the silicone adjacent to the substrate surface. Page 3 of The Dow Chemical Company. All rights reserved. Form No A

4 How To Use (Cont.) Base And Curing Agent Applications: Mixing The product contains a pigment which acts as an indicator for proper measuring and mixing. Thoroughly shake/stir the curing agent before use so that any sedimented pigment is redispersed. Weigh 100 parts of base and 10 parts of curing agent in a clean container, then mix together until the curing agent is completely dispersed in the base. Hand or mechanical mixing can be used, but do not mix for an extended period of time or allow the temperature to exceed 35 C (95 F). Mix sufficiently small quantities to ensure thorough mixing of base and curing agent. It is strongly recommended that entrapped air be removed in a vacuum chamber, allowing the mix to completely expand and then collapse. After a further 1 2 minutes under vacuum, the mix should be inspected and can be used if free of air bubbles. A volume increase of 2 3 times will occur on vacuum de-airing the mixture, so a suitably large container should be chosen. Note: If no vacuum de-airing equipment is available, air entrapment can be minimized by mixing a small quantity of base and curing agent, then using a brush, painting the original with a 1 2 mm layer. Leave at room temperature until the surface is bubble free and the layer has begun to cure. Mix a further quantity of base and curing agent and proceed as follows to produce a final mold. The base/curing agent ratio MUST be between 100:9.5 and 100:10.5. Base And Curing Agent Applications: Pouring The Mixture And Curing Pour the mixed base and curing agent as soon as possible onto the original, avoiding air entrapment. The catalyzed material will cure to a flexible rubber within 68 hours at room temperature (22 24 C/ F) and the mold can then be removed. If the working temperature is significantly lower, the cure time will be longer. Heat accelerating the cure is possible, but this will produce some apparent shrinkage of the mold due to differences in volume contraction on cooling between the silicone rubber and the original. The higher the curing temperature, the greater the likely differences in dimensions. Table 2: Pot Life And Cure Time Temperature C ( F) Working Time, Minutes Time To Cure 5 (41) > 360 > 24 hours 10 (50) hours 15 (59) hours 20 (68) hours 25 (77) 45 7 hours 30 (86) 30 4 hours 40 (104) 40 minutes 50 (122) 20 minutes Page 4 of The Dow Chemical Company. All rights reserved. Form No A

5 How To Use (Cont.) Base And Curing Agent Applications: Additional Information Inhibition Of Cure All addition-cured silicone elastomers are susceptible to cure inhibition when in contact with certain materials and chemicals. Inhibition has occurred if the elastomer is only partially cured after 24 hours, or has a sticky surface in contact with another material. Amines and sulphur containing materials are strong inhibitors, as are organotin salts used in condensation cure silicone elastomers. Wet or moist surfaces can cause gas bubbles to be formed during cure in the silicone adjacent to the substrate surface. It is strongly recommended that mixing containers, mold construction materials, originals and release agents be checked for any inhibition effect before use. Base And Curing Agent Applications: Use At High Temperatures Molds produced from SILASTIC RTV-4250-S Kit Green have a long life at elevated temperatures. However, continuous use above 200 C (392 F) will result in loss of elasticity over a period of time. Use above 250 C (482 F) is not recommended. When heated, a mold made of SILASTIC RTV-4250-S Base Green will expand producing a small change in copy dimensions. Base And Curing Agent Applications: Reproduction Of Vertical Surfaces If a skin mold is required of a vertical object or surface and cannot be made by normal pouring techniques, the catalyzed mixture can be made nonflowable by the addition of XIAMETER RTV-3011 Thixo Additive 1. Prepare the original as described earlier. 2. Brush the original with a thin layer of catalyzed mixture. Repeat the operation when the first layer has started to cure, to achieve a coating thickness of > 2 mm. Leave to cure at room temperature until the material is tacky. 3. Prepare a new catalyzed mixture of SILASTIC RTV-4250-S Kit Green and add 3% by weight of XIAMETER RTV-3011 Thixo Additive and mix thoroughly until a paste consistency is reached. De-airing of the mixture is not required. 4. Using a spatula, cover the coated original with the thixotropic coating until all undercuts are filled; leave to cure for 8 hours at room temperature. 5. Construct a support mold using polyester resin or plaster and allow to set in contact with the silicone coating. Carefully remove the support mold. Peel the rubber off the original and place in the support mold. Base And Curing Agent Applications: Resistance To Casting Materials The chemical resistance of fully cured SILASTIC RTV-4250-S Kit Green is excellent, and similar to all addition-cure silicone elastomers. It should be noted however that ultimately, resins and other aggressive casting materials will attack silicone molds, changing physical properties, surface release and possibly mold dimensions. Molds should be checked periodically during long production runs. Note: SILASTIC RTV-4250-S Kit Green is an industrial product and must not be used in food molding, dental and human skin molding applications. Page 5 of The Dow Chemical Company. All rights reserved. Form No A

6 Handling Precautions PRODUCT SAFETY INFORMATION REQUIRED FOR SAFE USE IS NOT INCLUDED IN THIS DOCUMENT. BEFORE HANDLING, READ PRODUCT AND SAFETY DATA SHEETS AND CONTAINER LABELS FOR SAFE USE, PHYSICAL AND HEALTH HAZARD INFORMATION. THE SAFETY DATA SHEET IS AVAILABLE ON THE DOW WEBSITE AT OR FROM YOUR DOW SALES APPLICATION ENGINEER, OR DISTRIBUTOR, OR BY CALLING DOW CUSTOMER SERVICE. Both base and curing agent can be sensitive to moisture and contamination. Ensure containers are tightly closed after. Usable Life And Storage Moldmaking Rubber Applications Product should be stored at or below 90 C (32 F) in original, unopened containers. Base and Curing Agent Applications Product should be stored at or below 25 C (77 F) in original, unopened containers. Limitations Health And Environmental Information This product is neither tested nor represented as suitable for medical or pharmaceutical uses. To support customers in their product safety needs, Dow has an extensive Product Stewardship organization and a team of product safety and regulatory compliance specialists available in each area. For further information, please see our website, or consult your local Dow representative. LIMITED WARRANTY INFORMATION PLEASE READ CAREFULLY The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer s tests to ensure that our products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent. Dow s sole warranty is that our products will meet the sales specifications in effect at the time of shipment. Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted. TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, DOW SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY. DOW DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES. Page 6 of 6 Trademark of The Dow Chemical Company Form No A